vespa 1956 1vl1t

hello, i bought years ago a Vespa and i will restore it. i 've a few question....

i will buy art 87989100 bush pascoli but there are no messures with article, is there somerbody how knows the messures of this ring (bush pascoli)???

i will hone the cilinder because the deflector piston without rings has too much tolerance. i will buy art 19431000 (meteor)(57.2) but i don't know what the messures must be when a buy a new piston. I can make the cilinder 57.2 mm , but what is the tolerance?? 57.18 to 57.2 mm??? 

And the qualite of meteor is good or are there better piston for my Vespa?

My English is not very good, i hope that somebody me can help, thanks carl